Electrical protective device



Patented Mar. 13, 1923,

umreo STATES DAVID T. MAY, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC PATENT OFFlCE.

COMPANY,

INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRICAL PROTECTIVE DEVICE:

Application filed December 6, 1920. Serial No. 428,544.

To all whom it may concern: Be it known that I, DAVID MAY, a citlzen of the United States, residing at New York city, in the county of New York, State of New York, have invented certain new and useful Improvements in Electr cal Protective Devices, of which the follow ng is a full, clear, concise, and exact description.

This invention relates to protective devices such as are used to protect delicate apparatus, and persons using the same from the injurious effects of unusually high electrical voltages, such as those inducedby ad ace nt unbalanced power circuits, lighting discharges and the like on the line circuits connected with the apparatus. 7

Such devices, as generally used, protect independently each side of the line. In case the dangerous current is induced 1n only one portion of the circuit, this form of protection is ordinarily adequate. However, when induction occurs in two separate portions of the circuit, one protector almost always acts first causing a sudden rush of current from the other side to the operated protector. A condition of this nature is dangerous on telephone circuits especially if persons are engaged in conversation when it occurs.

It is the object of this invention to prov de a simple and improved structure for a line protector device which will insure a substantially simultaneous discharge to ground of such excessive currents on the line.

In its preferred form, this structure 0on1 sists of a flat ground electrode surmounted by a porcelain block carrying two line electrodes spaced very closely so that when an arc occurs between one line electrode to the ground electrode, very little voltage is necessary to cause an are between the second line electrode and the first, thereby establishing a substantially common arcing space between the two line electrodes and the ground electrode. The voltage required to cause such a discharge is regulated by a spacing frame interposed between the ground electrode and the porcelain supporting block.

The invention will be morecoinpletely understood by reference to the drawing of the invention in the preferred form and which comprises Fig. 1 which shows a longitudinal section of the device, and a diagrammatic sketch of a simple circuit indicating the operation thereof; and Fig. 2 which shows a central cross-section of the same protector device. In the various figures, similar parts are indicated by similar reference characters.

Referring to the drawing, the carbon block 1 is provided with a flat surface upon which is placed a frame 2. Frame 2 is composed of a flat inwardly projecting shoulder 3 to rest against the carbon block and an upright shoulder 4. Within the upright shoulder 4, is laced a block 5 of insulating material preferably porcelain. a Centrally located in the block 5 is an aperture 6 into which two wedge shaped electrodes 7 and 8 are cemented. Electrodes 7 and 8 are placed so that their sharp edges 9 and 10, respectively, are very close together. Their opposin faces 11 and 12, respectively, are slight y bevelled so as to restrict to the edges 9 and 10 any arcing between them. The edges 9 and 10 are situated very close to the upper surface of the carbon block 1. The

.lower faces 13 and 14 respectively are also bevelled with respect to the upper surface of block 1 so as to further restrict the arcing between the electrodes 7 and 8 and the block 1. The lower surface of the porcelain block 5 is molded so that the lower edge projects to form a ridge 15 thereby forming a chamber between this under surface and the surface of the carbon block 1. The object of this chamber is to prevent short circuiting 0f the electrodes by particles of foreign matter collecting therebetween.

For the purpose of maintaining the electrodes 7 and 8 in engagement with their respective contact springs 16 and 17, shoulders 18 are molded on the upper edges of the porcelain block 5.

A suitable conductive plate 18 connected to ground is provided for completing a circuit from carbon electrode 1.

To show the advantage of this structure, the operation of this device will be described in connection with the circuit diagrammatically indicated in Fig. 1 in which 19 represents one line conductor of the circuit connected to the contact spring 17 of the electrode 8 and 20 represents the other line conductor connected with contact spring 16 of the lectrode 7. Resistance 21 represents apparatus included in the side 19 of the circuit between the contact spring 17 and the grounded terminal 23, and resistance 22 represents apparatus included in the circuit between circuit 16 and the grounded point 23. Beyond the protective device are located the primaries 24 and 25 of an induction coil (secondary not shown). Arranged in shunt with the primary 25 is a receiver 26.

The conductors 19 and 20 of the circuit, as is the usual practice in the telephone in stallations, are located in a cable so that induction due to unbalanced power lines in the vicinity would cause equal inductive efi'ects in both these conductors. If the potential of this induced current is sufficiently high,

to are between the point 10 of the electrode 8 and the grounded carbon block 1, the arc will be sufiicient to envelope also the point 9 and electrode 7. However, if the point 9 was not enveloped by this are, current would flow from the conductor 20, through the receiver 26, primary 24:, contact spring 17 and electrode 8 to the grounded carbon block 1 causing an extremely loud click in the receiver 26. The distance at which the points 9 and 10 are separated from the grounded electrode 1 depends upon the voltage against which it is desired to protect apparatus and this may be regulated by the thickness of the inwardly projecting edge 3 of the frame 2, and since this frame may be easily removed and replaced, the apparatus may be protected against any desired potential. distance between the electrodes 7 and 8 may also be widened if necessary by filing of the oints 9 and 10 to prevent arcing therebetween at normal voltages. It is preferable that the points 9 and 10 be placed very close together since after one of the electrodes has arced to the grounded block 1, the other electrode arcs to the first and thence to ground. The action of the two electrodes is practically simultaneous and almost no current flows through the receiver tltl) 26 under ordinary circumstances.

In case it is desired to protect, in a similar manner, a circuit having more than two conductors, it is understood that corresponding line electrodes of slightly altered shape may be located symmetrically within the aperture in the porcelain block to perform identically the same function as that described above. Such modifications are contemplated in this invention.

What is claimed is:

1. In an electric line protector device, an electrode adapted to be connected to ground, a pair of electrodes adapted to be connected to each side of the line wires, and means for so supporting said electrodes that their discharge surfaces and the surface of the ground electrode are substantially equidistant from each other to provide a substan tially common arcing space for the said electrodes.

2. In an electric line protector device, an electrode adapted to be connected to ground and comprising a plane-surfaced conductive block, a block of insulating material, a pair of electrodes adapted to be connected to the The incense line wires and supported by said block of insulating material at a very slight distance from the ground electrode and from each electrode connected to ground to form a substantially common arcing space for both of the electrodes connected to the line wires to the electrode connected to ground.

4. In an electric line protector device, an electrode adapted to be connected to ground and comprising a plane-surfaced conductive block, a block of insulating material provided with an aperture and having projecting lower edges with surfaces lying in a plane, a pair of wedge shaped electrodes, each of which is adapted to. be connected to one of the line wires and rigidly supported in the aperture of said block of insulating material so that the points of said electrodes are in close proximity and the adjacent surfaces recede from each other, and a spacing frame cooperative between the projecting edges of the supporting block and the ground electrode connected to ground to maintain the electrodes connected to the line wires at a predetermined distance from the electrode connected with ground.

5. In an electric line protector device, an electrode adapted to be connected to ground and comprising a plane-surfaced conductive block, a block of insulating material grooved upon its upper surface and having projecting lower edges with surfaces lying in a plane, an aperture being provided extending from the groove to the lower surface, a pair of downwardly extending wedge-shaped electrodes, each of which is adapted to be connected with the line wires supported within said aperture, the points of said line electrodes being in close proximity, and the adjacent faces receding from each other, and a spacing frame between the lower edges of the block of insulating material and the plane surface of the conductive block to maintain the electrodes connected with the line wires at a predetermined distance from the electrode connected with the ground.

In witness whereof, I hereunto subscribe my name this 29th day of November A. 1)., 1920.

M le 4" 

